The invention furthermore relates to a converter circuit, specified in the generic part of claim 2, to produce direct current with selectable polarity from a two-phase alternating voltage.
In the prior art, converters are known, which are designed as "rotary converters", in the form of a motor-generator set. In these known converters, the motor is thus driven by the three-phase current, and the direct current with the desired polarity and voltage is tapped from the generator, which is controlled by a control unit.
The commutators, which are present on the direct current side of these converters, are subject to wear. Increasing wear, on the other hand, favors the creation of sparks. For this reason, in installations which are sensitive to sparks, the converter must be maintained at regular intervals. In this way, maintenance intervals of about 40 days are necessary for converters, which run around the clock. This is associated with high costs.
A converter circuit of the generic type, in which the conversion is exclusively effected electronically and not by rotating pans, is known from the IP-58157389 (Patent Abstracts of Japan, Volume 7, No. 280, E-216). This converter circuit has no rotating parts and consequently is absolutely free of wear, and thus needs little maintenance. The known converter circuit of this kind consequently greatly surpasses "rotary converters" with regard to reliability, and consequently is especially suitable for applications, for which a continuous operation with a high reliability is important. However, it has the disadvantage that the production of a continuously variable direct voltage presents difficulties.